Typically, as shown in FIG. 1, a wireless communication system comprises elements such as client terminals or mobile stations and one or more base stations. Other network devices may also be employed, such as a mobile switching center (not shown). As illustrated in FIG. 1, the communication path from the base station (BS) to the client terminal or mobile station (MS) is referred to herein as a downlink (DL) direction or downlink channel, and the communication path from the client terminal to the base station is referred to herein as an uplink (UL) direction or uplink channel. In some wireless communication systems, the MS communicates with the BS in both the DL and UL directions. For instance, such communication is carried out in cellular telephone systems. In other wireless communication systems, the client terminal communicates with the base stations in only one direction, usually the DL. Such DL communication may occur in applications such as paging. As used herein, the terms “base station” and “network” are used interchangeably.
Normally, the transmission intervals in the downlink channel or in the uplink channel span certain predefined duration and it is referred to as “frame” herein. Frame duration may be different for different communication systems and normally it is on the order of a few milliseconds. For example, the frame duration may be five milliseconds. Typically in a wireless communication system, the client terminal and the base station may transmit information in blocks of data and such a block of data is referred to herein as a “message.”
A base station to which the client terminal may be downlink synchronized and/or communicating with at any given time is referred to herein as the Serving Base Station (SBS). In some wireless communication systems the serving base station may be referred to as the serving cell. The base stations that are in the vicinity of the serving base station are called Neighbor Base Stations (NBS). Similarly, in some wireless communication systems a neighbor base station may be referred to as a neighbor cell.
A client terminal, after initially synchronizing with a cell, may switch to another cell depending on the signal conditions, network congestion, and other criteria. The process of switching from one cell to another cell by a client terminal is often referred to as handover (HO) or cell reselection. In some wireless communication systems handover is also referred to as handoff. Also in some wireless communication systems cell reselection is also referred to as idle mode handoff. An NBS, to which a client terminal may be switching over its communication from the current SBS, is herein referred to as Target Base Station (TBS). In some wireless communication systems, a target base station is normally referred to as a target cell. Sometimes, during a handover, the serving cell and the target cell may be the same and only the channel used for communication may be changed. Such a handover, in which the cell is not changed, is called an intra-cell handover. The purpose of intra-cell handover may be that the new channel is better suited for communication than the previous channel within the same cell. Cell reselections or handovers amongst cells that use the same frequency are referred to herein as intra-frequency cell reselection or handover. Cell reselections or handovers amongst cells that use different frequencies are referred to herein as inter-frequency cell reselection or handover.
The decision making process for handovers and cell reselections varies from one wireless communication system to another. However, the decisions are generally based on the signal conditions measurements by the client terminals and reporting of those measurements to the wireless communication network by the client terminals. The wireless communication network generally may influence and control the measurements and reporting process of the client terminal by providing parameters for the measurement and reporting process. The actual decision to perform handover may be made either by the wireless communication network or by the client terminal depending on the type of particular wireless communication system. On the other hand the cell reselection decisions in idle mode (i.e., when client terminal is not in active communication with the wireless communication network) may be generally performed autonomously by the client terminal. Both handovers and cell reselections may normally lead to change of cell from which the client terminal may access communication services. The difference between the handover procedure and cell reselection procedure depends generally on whether a client terminal is engaged in an active communication with the wireless communication network.
Normally, certain types of system information may be required by all client terminals so that they may communicate with the wireless communication network. The system information typically includes system synchronization information, system parameters, resource allocation information, paging information, etc. The wireless communication network may transmit such system information as broadcast data so that all client terminals within its coverage area may be able to receive the system information. Such information is herein referred to as “broadcast messages.”
Typically in a wireless communication system a base station may group the system information and each group of system information may be transmitted as multiple broadcast messages and such broadcast messages are herein referred to as system parameter messages. The system parameter messages may carry important system information without which the client terminal may not be able to communicate with the wireless communication network. The wireless communication network may transmit these system parameter messages at regular intervals in such a way that any client terminal that enters its coverage area may receive these system parameter messages and may be able to communicate with the wireless communication network at the earliest possible time. Client terminals that are already in the base station's coverage area may also periodically receive these system parameter messages for possible updates. Normally a client terminal may store the system parameter messages in its memory for the current SBS.
Typically, in wireless communication systems, most of the system parameter messages may not change frequently. For example, some system parameter messages may change once or twice a day and some system parameter messages may not change for many days.
In some wireless communication systems, when a client terminal switches to a new base station due to cell reselection or handover, it may be required to receive the system parameter messages for the new SBS and certain system parameter messages for the selective list of NBSs corresponding to the new SBS.
The set of all system parameter messages broadcast by a base station is herein referred to as “base station broadcast system information.” The individual block of system information message may be referred to as System Information Block (SIB). Two or more SIBs may be grouped and sent as a single System Information (SI) message. There may be different SIBs describing different groups of system parameters such as SIB Type1 (SIB1), SIB Type2 (SIB2), etc.
Each base station in a wireless communication network may be identified by a unique identifier referred to herein as Cell Identity (CID). The CID of a base station may become known to a client terminal when it decodes SI from the base station. To avoid unnecessary updates from a client terminal and yet ensure the ability to reach a client terminal at any given time, the network may organize a group of cells into a “tracking area” and use a Tracking Area Identity (TAI) to identify the various groups of cells. This is illustrated in FIG. 2 where four different tracking areas are illustrated. A cell may broadcast information about the tracking area it belongs to by including the TAI information in the SI. A client terminal may be required to inform the network when it begins to receive service from a cell that belongs to a tracking area that is different from the tracking area of the cells from which it was previously receiving service. The process of informing the network that the client terminal has begun receiving service from a cell that belongs to a new tracking area is referred herein as Tracking Area Update (TAU) procedure. With this method, a client terminal performs TAU only when there is a change in TAI of the cell from which it is getting service. For example, in FIG. 2, when a client terminal reselects from the cell with CID=1003 to the cell with CID=1007 which has the same TAI, it may not perform TAU procedure. However, when the client terminal reselects from the cell with CID=1007 and TAI=200 to the cell with CID=1012 and TAI=201, it may perform TAU procedure.
A client terminal may need to initiate the connection establishment procedure with the wireless communication network using the system parameters provided from SIBs to access the common control channels, such as Random Access Channel (RACH), Random Access Response, etc., in its current serving cell under different example conditions as follows: (i) when a client terminal performs cell reselection to a cell not belonging to a tracking area in its set of registered tracking areas, (ii) when there is a need for periodic TAU after cell reselection due to its periodic timer expiry, (iii) if a client terminal receives a mobile terminated call, and (iv) when a user initiates a mobile originated call. In case of a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) wireless communication system, the common control channel parameters are provided in SIB2. Unless SIB2 is received for its current serving cell, a client terminal may not initiate its connection establishment procedure. Hence there may be a delay in the connection establishment procedure when the client terminal does not have a valid SIB2 for the cell. In different wireless communication systems, the common control channel parameters may be provided in different system information blocks.